17-459: See text The Actinoceriatidae are a family of actinocerids named by Saemann in 1853 for those that grew to have large shells with blunt apices and large siphuncles with widely expanded segments and a generally arcuate endosiphucular canal system. Their range is from the upper Middle Ordovician to the Lower Silurian . Actinocerids are generally straight-shelled nautiloid cephalopods with
34-633: A siphuncle composed of expanded segments, typically with thin connecting rings, in which the internal deposits are penetrated by a system of canals Actinoceratids are derived from Wutinoceras , possibly through an early Armenoceras or through Nybyoceras and give rise to Lambeoceras and to the Huroniidae. Seven genera are included in the Actinoceratidae, Actinoceras , Floweroceras , Kochoceras , Leurorthoceras , Paractinoceras , Saffordoceras , and Troostoceras . Actinoceras
51-524: A system of radial canals and a narrow space along the inner side of the connecting ring known as a paraspatium. (Teichert 1964) Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm (2.0 to 3.0 ft) but some, like the Huroniidae of the Silurian grew significantly larger. The Actinocerida inhabited shallow to quite deep waters, where they alternated between swimming and lying on
68-454: Is doubtfully distinct from Kochoceras . Leurothoceras is synonymous with Actinoceras ; Saffordoceras and Troostoceras are closely related. Actinocerida The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic , distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain
85-576: Is probably the most distinct actinoceratid from Actinoceras . Paractinoceras has a long, straight, slender shell and a siphuncle that starts off like that in Actinoceras , but becomes narrow like that in Ormoceras in the anterior part of the phragmocone. Kochoceras has a large blunt shell that expands more rapidly than Actinoceras and is strongly flattened on the ventral side causing possible confusion with Lambeoceras to casual observation. Floweroceras
102-615: Is the earliest but with a range that carries it into the Lower Silurian. Troostoceras followed by Saffordoceras are later Middle Ordovician genera related to early Actinoceras . Kochoceras followed by Floweroceras are Upper Ordovian genera related to later Actinoceras . Leurothoceras and Paractinoceras , both from the Upper Ordovician, are shown to have their source in Middle Ordovician actinoceratids. Paractinoceras
119-521: The siphuncle , distinguishing it from later forms with arcuate canal systems. Septal necks, components of the siphuncle that project from the back side of the septa, are cyrtochoanitic (outwardly curved) and may be recumbent. Connecting rings are thick, reflective of the ancestral form. The three varieties of Wutinoceras are based on the form of the siphuncle, and each contains a number of species. These have not been ascribed to subgenera. They include those with broad segments and strongly recumbent brims to
136-582: The Armenoceratidae and Huroniidae extend into the Upper Silurian. The Ormoceratidae are possibly the most recent, extending into the Lower Devonian Gonioceras (Gonioceratidae) is limited to the Middle Ordovician, its quasi-lookalike Lambeoceras (Lamberoceratidae) to the uppermost Middle and Upper Ordovician. The wutinocerids are known only from the early Middle Ordovician (Whiterockian) and
153-882: The Georginidae, which are known from the Cassinian in Northern Australia. They reached their greatest diversity in the Middle Ordovician with more than 20 genera, then declined somewhat in the Late Ordovician and more so in the Early Silurian ; made a slight come back in the Middle Silurian but not to Late Ordovician numbers; and declined more or less steadily from the Late Silurian into the Devonian. Three major lineages began
170-493: The Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from Wutinoceras and the Ormoceratidae from a second wutinocerid genus, Adamsoceras . Gonioceras is an offshoot of an early Armenoceras; Lambeoceras and Huronia are offshoots of a later Actinoceras . The Actinoceratidae extend into the Lower Silurian with Actinoceras ;
187-412: The ancestral form of the actinocerids, and was derived from the ellesmeroceriid Bathmoceras . However, it turned out based on a reassessment of Lower Ordovician and Whiterockian formations in northeastern China that Polydesmia is antedated by Wutinoceras , its assumed primitive nature rather a derived condition. Actinocerids first appeared early in the Middle Ordovician, with the exception of
SECTION 10
#1732887658776204-612: The bottom. They were predatory, and able to control their buoyancy to a greater degree than their contemporaries. The derivation of the Actinocerida remains enigmatic. They first appear late in the Early Ordovician (Cassinian Stage, late Floian) with the Georginidae but don't become well established until the beginning of the early Whiterockian Stage (Dapingian) of the Middle Ordovician (Flower 1868,1976) The Georginidae, introduced and described by Mary Wade in 1977 (Wade 1988), based on
221-520: The genus Georgina , are known from the upper Canadian Coolibah Formation of the Georgina Basin in Northern Australia. How the Georginidae relate to older stocks is unclear. The Upper Cambrian Protactinocerida have been suggested as being ancestral but none are known to have gone beyond the near end of the Cambrian extinction, which makes any connection hypothetical. Polydesmia was once thought to be
238-615: The polydesmiadids are restricted to about that time. Originating in the Ordovician, by the Devonian period actinocerids became rare; perhaps they were unable to compete with the more compact and maneuverable coiled nautiloids and ammonoids and cope with the arrival of jawed fish. The Actinocerida contain nine families; the Georginidae, Wutinoceratidae, Polydesmiidae, Armenoceratidae, Ormoceratidae, Actinoceratidae, Gonioceratidae, Lambeoceratide, and Huroniidae. The Carbactinoceratidae, included in
255-575: The septal necks; those with large segments and rings free ventrally; and those with small segments in which the brims on the dorsal side are sometimes free. The genotype Wutinoceras foerste , which comes from northeast China ( Manchuria ), is of the second variety. Wutinoceras species of the broad-segment variety are found in Newfoundland, Oklahoma, and Tasmania; those of the large-segment variety are found in Utah, Nevada, Newfoundland, and Manchuria. Those of
272-452: The small-segment variety have only been found in Nevada. unless new species described from elsewhere can be included. Wutinoceras may have its origin in the primitive actinocerid Georgina from the upper Lower Ordovician of Northern Australia and east Asia although its exact ancestor remains elusive. Wutinoceras was once thought to be derived from Polydesmia from northern China, which
289-636: The taxonomy in the Treatise, (Vol K) have been removed to the Pseudorthocerida. Wutinoceras Wutinoceras is a genus of now extinct nautiloid cephalopods of the Wutinoceratidae family. It exhibits orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments. Wutinoceras , as with its family the Wutinoceratidae, has a reticulated canal system within
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